• Composites Research
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• v.24 no.2
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• pp.38-45
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• 2011

In this paper, we present an optimization method for the single Dallenbach-layer type microwave absorbers composed of E-glass fabric/epoxy composite laminates. The composite prepreg containing carbon nanotubes (CNT) was used to control the electrical property of the composites laminates. The design technology using the genetic algorithm was used to get the optimal thicknesses of the laminates and the filler contents at various center frequencies, for which the numerical model of the complex permittivity of the composite laminate was incorporated. In the optimal design results, the content of CNT increased in proportion to the center frequency, but, on the contrary, the thickness of the microwave absorbers decreased. The permittivity and reflection loss are measured using vector network analyzer and 7 mm coaxial airline. The influence of the mismatches in between measurement and prediction of the thickness and the complex permittivity caused the shift of the center frequency, blunting of the peak at the center frequency and the reduction of the absorbing bandwidth.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.51-57
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• 2010

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.2
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• pp.34-42
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• 1998

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.244-249
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• 2008

In this paper, we designed and fabricated the EM wave absorber consists of Sendust and Mn-Zn ferrite for suppressing EM wave noise from PCB in ISM(Industrial, Scientific and Medical) band of 2.4 GHz. We fabricated several samples in different ratios of Sendust to Mn-Zn ferrite with CPE(Chlorinated Ploy-ethylene) as binder and confirmed that optimum composition ratio of absorbing materials was Sendust. Mn-Zn ferrite : CPE=70:5:20 wt.%. The absorbing abilities were simulated according to different thickness of EM wave absorber as the function of material constants calculated by measured data. Measured absorption ability was analyzed and compared with simulated result. The simulated result agree well with the measured ones. As a result, the developed EM wave absorber with thickness of 0.85 mm has absorption ability of 5.4 dB at 2.4 GHz and over 3 dB in frequency rage of 1.4$\sim$4.1 GHz.

• Composites Research
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• v.23 no.2
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• pp.17-23
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• 2010

The stealth technology can increase the survivability of aircrafts or warships and enhance the capability of mission completion in hostile territory. The purpose of this paper is to present the low observable structure with curved surfaces made by fiber-reinforced composites and to show the possibility of developing omnidirectional stealth platforms for military applications. In this study, we developed a radar absorbing structures(RAS) based on a circuit analog absorber to reduce the radar cross section(RCS) of an object with curved surfaces. Firstly, the RAS with a periodic square patterned conducting polymer layer was designed and simulated using a commercial 3-D electromagnetic field analysis program. Secondly, the designed semi-cylindrical structure with low RCS was fabricated using fiber-reinforced composites and conducting polymer. To make the periodic pattern layer, acts as resistive sheet, the intrinsic conducting polymer paste containing PEDOT with a polyurethane binder was used. Finally, the radar cross section was measured to evaluate the radar absorbing performances of the fabricated RAS by the compact range facility in POSTECH.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.161-164
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• 1998

광대역 주파수 상에서 외부로부터 입사하는 전자파를 산란시키지 않고 유전체 내부에서 흡수시키기 위해 유전체를 다층으로 배열하여 전파 흡수체를 최적 설계하고자 한다. 수직 및 여러 각도로 전파가 입사하는 경우 각 유전층의 두께, 유전 상수, 손실 탄젠트 등의 설계변수를 유전자 앨거리즘을 이용하여 최적화한다. 다극함수에서의 부분 초기화 유전자 앨거리즘의 성능 향상을 위해 부분 초기화율, 부분 초기화 시점, 스케일 인자의 변화에 따른 성능을 비교, 개선하여 흡수체 설계에 적용하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.4
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• pp.346-352
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• 1996

A wide-band design method of double layered electromagnetic wave absorbers cross-slotted in the second layer(which has very wide band frequency characteristics) is proposed and discussed. The wide-band electromagnetic wave absorber can be designed under some approximations by the the- oretical model using the equivalent material constants method applied to the second layer. Based on the developed model, wide-band electromagnetic wave absorbers with excellent reflectivity characteristics in the frequency range of 30MHz to 3, 170MHz were designed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1329-1334
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• 2003

We prepared EM wave absorbers by using recycled Ba ferrite far GHz frequency, and investigated the effects of carbon additions and preparation temperatures on their EM wave absorption properties. We clarified that it is very important to consider carbon amounts in Ba ferrite and preparation temperature for Ba ferrite EM wave absorbers with high quality.

• Korean Journal of Materials Research
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• v.5 no.5
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• pp.512-517
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• 1995

EMI 대책용 전자파 흡수체로 알려진 cu-Ni-쿠 페라이트를 분말야금법으로 제조하여, 성형압력과 소결온도의 변화에 따른 미세조직을 과낯ㄹ하고, 투과반사법으로 전자파 흡수능을 측정하여 조직과의 관계로 검토하였다. 하소는 공기중에서 90$0^{\circ}C$로 2시간동안 행하는 것이 최적이었다. 미세조직과 입자의 크기는 성형압과 소결온도로 제어할 수 있다. 100Mpa로 성형한 것이 치밀하고, 전자파 흡수특성이 우수하였다. 복소유전율과 복소투자율은 기공도와 소결밀도에 영향을 받았다. 전자파흡수능은 밀도보다는 입자의 크기에 더 큰 영향을 받았다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1995.11a
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• pp.88-93
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• 1995

연소 배가스에서 NOx 제거시 분자 분해를 위하여 Microwave Energy를 이용했다. 이는 전자파를 흡수하는 고체물질에 전자파를 조사할 때 내부로 부터 가열이 이루어지는 특성과 전파의 진동에 의한 분자내 쌍극자가 진동하는 현상을 이용하여 분자결합이 깨지는 현상을 응용한 것이다. 전자파흡수체로서 Calcined Char를 사용했으며, 표준가스로는 NO 574 ppm을 2$\ell$/min으로 통과시키면서 2450 MHz의 전자파를 조사했을 경우 95 % 이상 분해 제거가 가능했다. 보다 낮은 농도의 연소배가스에 대해서는 거의 완전한 제거가 가능하므로 대기환경오염방지에 일조할 것으로 기대된다.